A grinding machine is a self-propelled or portable machine that is used to reduce trees, brush and other materials by tearing, shredding, impacting or shearing such materials to a relatively uniform particle size. A horizontal grinding machine typically has a hopper for feed material at the front of the machine and a feed mechanism for advancing material from the front hopper to a grinding mechanism in a generally horizontal direction. The feed mechanism may include a feed conveyor at the bottom of the hopper and one or more feed roller assemblies located above and in front of the grinding mechanism. The grinding mechanism usually comprises a drum or series of discs having cutting components disposed around the periphery. A grate is also typically located behind the grinding drum or discs to provide some measure of control over the particle size of the material being reduced. A discharge chute or conveyor is located adjacent to and behind the grinding mechanism to channel or convey material that has been reduced by the grinding mechanism away from the machine. A power source that may include an internal combustion engine and a hydraulic circuit containing one or more hydraulic motors is provided to power and operate the grinding mechanism, feed mechanism and (if provided) the discharge conveyor.
The production rate of a horizontal grinder is maximized when the feed mechanism is operated to maximize the processing of material through the machine without contributing to or causing stalling due to overfeeding. The production efficiency of a horizontal grinder is maximized when the feed mechanism is operated so as to limit material flow to a steady predetermined rate that gives the greatest production output per unit of fuel burned. Engine overloading is avoided when the feed mechanism is operated to limit material flow so the power required to reduce the material is equal to or less than the allowable continuous power output of the engine. When grinding feed materials of varying sizes, using conventional machines and methods, it is impossible to maximize production efficiency or to regulate power demand by controlling the feed rate. However, feed rate control methods may be employed to maximize production rates and efficiencies without overloading the engine when grinding feed materials having a uniformly small particle size range.
Grinding to reduce previously reduced material to an even smaller particle size is termed re-grinding. Because re-grinding processes previously-reduced material, the production rate and efficiency of a grinding machine engaged in re-grinding may be maximized without overloading the engine by controlling the feed rate. Re-grinding produces the most desirable product when the grinding mechanism is fed at a constant rate to keep the grinding chamber full but not flooded with material. This feed rate is termed “choke feeding”, and it is particularly important when re-grinding of woody materials is used to create mulch, especially mulch to which a colorant or other additive is applied. Choke feeding in the creation of mulch will generally insure that the colorant or additive is uniformly distributed in the final mulch product.
The feed rate of a grinding machine engaged in re-grinding can be further controlled for maximum efficiency or to limit engine power demand. Such feed rate control is termed “regulated feeding”. Regulated feeding enables the engine to operate at a controlled rate, thereby optimizing fuel use and maximizing the operating life of the engine.
Controlled feeding in a grinding machine can be achieved by pinning the feed roll assembly at a fixed height with respect to the grinding mechanism or by using a leveling bar ahead of the feed roll assembly to limit the height of the feed stream into the grinding mechanism. However, pinning the feed roll assembly in a raised position may impede the safety characteristics of the feed roll assembly, and a leveling bar is an added component to the machine. Furthermore, neither of these known methods for achieving controlled feeding permits control of the maximum continuous power output of the engine so as to increase engine life and maximize fuel efficiency. Consequently, it would be desirable if other systems and mechanisms could be provided for maintaining choke feeding or regulated feeding during operation of a grinding machine.